Since its inception the goal of this project has been to understand how HLA class I polymorphisms modulate the immune response to viral infections and transplanted tissues. Initially, the cytolytic T cells of adaptive immunity formed the functional context for the research. They are now joined by the natural killer (NK) cells of innate immunity, which are also regulated by cell-surface receptors that interact with HLA class I determinants. These receptors consist of two kinds: CD94:NKG2 and killer cell inhibitory receptors (KIR), encoded by gene families unlinked to the HLA complex. Within individuals, expression of different receptor combinations by subsets of NK cells creates diverse NK-cell repertoires. Such repertoires are influenced by the HLA types of individuals and also by differences in their KIR. Whereas knowledge of HLA class I polymorphism is fairly complete, that of KIR is rudimentary. An initial survey reveals diversity in KIR phenotype, due both to the types of KIR genes, as well as their allelic polymorphism. A systematic analysis of KIR gene diversity will in four Aims test hypotheses emerging from the initial survey. To define individual KIR haplotypes, recently developed DNA typing methods will be used in Aim 1 to track the segregation of Kir genes in families. In Aim 2, a multiethnic panel of B-cell lines will be analyzed by Southern blotting and DNA typing. This approach will assess the extent of KIR genotype and haplotype diversity in the human population. Aim 3 will define the extent of allelic polymorphism at each of the Kir genes by cDNA cloning and sequencing. Analysis of these sequences will place KIR diversity in the context of the three-dimensional structure of KIR glycoproteins and their function, and assess the importance of natural selection. An expanded database of accurate KIR nucleotide sequences will permit design and development of high-resolution KIR typing, applicable to the study of populations, disease associations and clinical outcome in transplantation. Aim 4 is a study of KIR in Native Americans, populations whose genetic diversity is most likely due to natural selection rather than population admixture. This study will provide a yardstick for KIR diversity in other populations, assess KIR diversity that can be maintained under natural selection, and determine whether KIR have, like HLA class I, undergone rapid evolution in South America. The proposed investigation of KIR diversity will greatly benefit from prior experience with HLA class I diversity, and will complement genomic analyses of the KIR gene family from other laboratories. Collectively, the four Aims should give a picture of KIR diversity and an understanding of how polymorphic KIR and their HLA class I ligands assort in human population to produce NK-cell receptor repertoires.